usb: dwc3-msm: Mask events on cable disconnect

If erratic event occurs upon cable disconnect, then controller is
generating erratic events even after block reset is done.
Hence prevent this situaton by masking all events on cable disconnect
and after handling first block reset.
Blocking the subsequent events would later prevent
the unclocked register access due to controller suspend turning
off core clock while block reset work is in progress.

CRs-fixed: 754183
Change-Id: Iab364f0f72bc467067471835101a4931f786e61e
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>